1. Field of the Invention
This invention relates generally to tools for setting fasteners having pin members with pull grooves and more particularly concerns a rotatable nose assembly for lockbolt installation tools. The nose assembly is designed to minimize deflection between a collet and anvil during swaging of a collar about a pin member and to minimize operator fatigue by facilitating the positioning of the nose assembly about a lockbolt.
2. Description of Prior Developments
A demand has arisen for an ergonometrically designed installation tool for setting fasteners of the lockbolt type. A tool is required which can access and install lockbolt fasteners located between closely spaced panels or within a small clearance space. To satisfy this demand, various attempts have been made to provide an offset nose assembly including an anvil and collet for swaging a fastener collar about a grooved fastener pin. In various prior designs, the axis of the swaging anvil has been radially offset from the axis of the piston which drives the anvil against the collar. This arrangement allows the radially offset anvil portion of the nose assembly to access and set fasteners without interference from the anvil housing and/or from the body of the installation tool.
By offsetting the axis of the fastener pin and collar assembly from the axis of the tool piston, large bending forces are generated within the nose assembly during swaging of the collar around the pin. These bending forces have heretofore resulted in deflection between the anvil and collet as well as deflection of the entire nose assembly with respect to the body of the installation tool and with respect to the pin and collar. This deflection, which arises primarily from assembly tolerances and loose fit threaded joints, results in the application of a radial force to the pin and has causes radial deflection of the pin during setting of the fastener.
Such radial deflection, when transmitted and applied to the fastener pin, has caused premature and/or uncontrolled pin breakage resulting in defective connections between the pin and collar. This problem is particularly acute when titanium alloyed pins are used since these pins are most sensitive to radial loading and will easily shear under such radially applied loads before the collar is fully set.
Another problem caused by the deflection between the anvil and collet is the rapid wear between these moving parts. Wear can become particularly acute between threaded joints. As the parts wear, they lose their ability to properly set the collar about the pin. Conventional nose assemblies often wear out prematurely thereby necessitating replacement of the worn parts at relatively frequent intervals. This further reduces productivity and incurs significant replacement costs.
To prevent these undesirable results, prior designs have attempted to resist the deflection of offset nose assemblies by increasing the size and mass of the anvil housing, the collet and the threaded collet stud which connects the collet to the tool. These massive and bulky assemblies thus attempted to provide the necessary rigidity within the nose assembly per se. While such designs have generally performed satisfactorily, they have not been able to access extremely close or cramped installation sites due to their relatively large and massive construction. That is, in order to stiffen the nose assembly, prior anvil housings and collets have been designed with thick cross sections thereby resulting in relatively bulky and wide contours incapable of reaching within small spaces.
Even with an offset nose assembly, certain installation sites necessitate awkward and uncomfortable tool manipulations in order to access and set the lockbolt fasteners. Because installation tools can weigh from 8 to 15 pounds and must be hand operated in cramped locations, an operator can quickly experience muscle fatigue. This fatigue results in lower production rates and promotes defective lockbolt joints since a fatigued operator is prone to misalign the tool during setting of the fastener.
In some cases, an installation site is so inaccessible that the use of pin and collar lockbolts is precluded because the lockbolt installation tools cannot access the installation site. The conventional solution to this problem is to install threaded fasteners of the nut and bolt variety with a hand tool such as a wrench or the like. This approach is not only time consuming and expensive, it is also inefficient as retorquing is often necessary after installation.
Accordingly, a need exists for an ergonometrically designed durable rotatable offset nose assembly which resists deflection and wear under load, prevents undesirable pin deflection, avoids premature and/or uncontrolled pin failure and allows access of the nose assembly within tight or cramped spaces without causing operator fatigue.